Ductility of dispersed phase alloys,particularly al-al2o3



United States Patent US. Cl. 148-11.5 12 Claims ABSTRACT OF THEDISCLOSURE The ductility of dispersed phase alloys, more particularlyAl-Al O is improved by a process wherein an ingot is produced byspraying the dispersed phase alloy powder or wire onto a base (basis)body at a temperature of at least 800 C. and wherein the thus obtainedbillet is submitted to degassing and oxide stabilization at atemperature of about 550-625 C. in a vacuum furnace (10 to 10 mm. Hg)for from to 30 hours. The billet is then ready for fabrication intofinished products. Normally the billet is removed from the base bodybefore it is submitted to mechanical working, but in some cases themechanical working is effected without removing the billet from the basebody.

This invention relates to a process for improving ductility ofmetal-oxide composite materials or dispersed phase alloys and speciallyconcerns aluminum-alumina composite material.

As it is known, the aluminum-alumina composite material generally usedis sintered Al-Al O a metallurgical composite of the dispersed phasealloy type, Which offers multiple advantages for various purposes, suchas for example, canning material for fuel elements of certain types ofnuclear reactors.

This material is prepared principally in the following way: a powder ofaluminum is partially oxidized to A1 0 The part of weight of A1 0 in theoxidized powder can vary from 2% to 20%. The oxidized powder is firstcold compacted and then sintered to form an ingot or billet.

Preferably, before sintering, the compacted powder is degassed; thesintered ingot or billet is then metallurgically processed, by way of atleast one extruding process, in order to achieve the needed propertiesof a semi-finished or finished product.

Within the scope of manufacturing nuclear fuel elements cladding usingthis Al'Al O material, it is now well known that this material possessesgood mechanical characteristics of thermal resistance, which were alsoproved by means of long term tests.

However its use is actually limited to the manufacture of fuel elementscladding in the form of a self-resistant rigid can because of the lackof creep ductility which this material shows.

By way of example, tensile and creep tests carried out at 450 C. withspecimens of sintered Al-Al O yield the following mean values.

Example 1.-Extruded bars of sintered Al--Al O;, containing 4% aluminaTensile tests (fast traction) Ultimate tensile strength: R=6 kg./mm.

Patented Nov. 4, 1969 ICC 0.2% yield limit (strength): S =5.5 kg./mm.Total elongation percent (5 diameters): A =6% Creep tests at 1000 h.

Rupture stress a 4 kgJmm.

Total elongation percent (5 diameters) A, 0.5%

Example 2.--Extruded bars of sintered Al-AI O containing 7% aluminaTensile tests (fast traction) Ultimate tensile strength: -R=8 kg./mm.0.2% yield limit (strength): 8 :7 kg./mm. Total elongation percent (5diameters): A =4% Creep tests at 1000 h.

Rupture stress :7 5 kgJmm.

Total elongation percent (5 diameters) A5 0.7%

The elongation before rupture is about 0.5%.

Example 3.-Extruded helical finned tubes of sintered Al-Al O containing7% alumina Tensile tests (fast traction) Ultimate tensile strength:R=8.5 kg./mm. Total elongation percent (5 diameters): A =4% Burst testBursting stress: a-=7 kg./mm.

The value of elongation at rupture A which generally is less than 1% forAl-AlgOg materials of different oxide content too, is veryrepresentative of the very low creep ductility of the material.

Hence the interest of improving this creep ductility accompaniednevertheless by the aforesaid good mechanical properties, as far as theuse of this material for nuclear purpose is concerned, in order to makefrom this material fuel element claddings, the claddings having the formand properties of resistant and ductile sheaths.

We have found that composite material Al-Al O containing from 2% to 20%of weight of alumina, of improved ductility, principally creepductility, is obtained by a process which, according to the presentinvention, is characterized in that an ingot or billet. is produced fromAl-Al O -powder or -wire by metal-projection or spraying of the sameonto a basis body, and that the billet is then submitted tometallurgical transformation, by mechanical working in order to achievethe final mechanical properties for semi-finished or finished products.Use can be made of oxidized powders A1-Al O or alternatively ofsemi-finished sintered hot compacted composite material Al-Al O thelatter being previously reduced from the original diameter of a bar oran ingot or a billet to fires of a small diameter by way ofwire-extrusion and following wire-drawin operations.

The diameter size of the wires obtained from ingots, the diameter ofwhich is normally comprised between 70 and 20 mm., to be used for themetal projection is comprised between 1 and 10 mm.

The metal projection is carried out at a distance varying from 50 mm. to250 mm. from the basis body.

The projection direction can vary from perpendicular to parallel withrespect to the bodys axis, the parallel direction being preferred.

The projection should be executed at a temperature of about at least 800C. and within strictly limited projection periods of some seconds, orpreferably less than one second.

The prepared billet is to be submitted to thermal degassing and oxidestabilization in a vacuum furnace.

These operations should be eflected at temperatures varying from 550 C.to 625 C., at a residual pressure comprised between 10 and 10 mm. Hg,for periods of 10 to 30 hours, preferably of 20 to 24 hours.

The semi-finished or finished products, as bars, smooth or finned clads(with right or straight or helicoidal fins) are particularly obtained bymetallurgical operations as known for usual production, comprising forinstance extrusion and eventually drawing with intermediate annealing.

In order that the invention may be more readily understood, fourspecific embodiments of the same will now be described by way ofexample.

Embodiments 1 and 2.-4% Al-Al O 7% Al-Al O A first ingot or billet ofsintered AlAl O material with 4% r 7% of alumina, obtained by normalfabrication, having a diameter of 70 mm. was wire-extruded at atemperature of about 570 C. through a die to obtain mm. diameter barsand then these bars were wire-drawn at room-temperature to provide in 3or 4 runs 3 mm. diameter Wires.

These wires were projected by means of a metallising gun (Mark Metco) tocreate a new billet.

The metal projection was effected at the following operating conditions:

Oxygen (O flow rate 50 liters/minute.

Acetylene flow rate 50 liters/minute. Compressed air pressure 4.5kg./cm.

Projection distance About 100 mm.

Projection direction At a right angle to the axis of the billet inpreparation.

The projection operation was stopped when a billet had been obtainedwith a thickness of about 2 cm. sufiicent to permit its working by meansof a lathe in order to obtain an entirely cylindrical surface.

After this cylindrical turning or grinding the projection operation waspursued until a billet of about 70 mm. diameter was obtained. Thisbillet was turned on a lathe to a diameter of 68.4 mm. and then degassedin a furnace under high vacuum, namely of 10- mm. Hg, by heating at atemperature of 600 C. during 20 hours.

The degassed billet was then extruded through a die at 520 C. to provide20 mm. diameter bars.

The extrusion data were:

Container diameter: 70 mm. Container temperature: 500 C. Dietemperature: 480 C. Extrusion ratio: 12.3

Extrusion speed: 7.38 m./min.

In the case of 4% Al-Al O the tensile and creep tests were carried outat 450 C. to yield the following average values:

Tensile test (fast traction) Ultimate tensile strength: R=6 kg./mm. 0.2%yield limit (Strength); S =5.5 kg./mm.

Total elongation percent (5 diameters): A =15% Creep test at 1000 h.

Rupture stress e 4 IrgJJzmn.

Total elongation percent (5 diameters) A5 15% It can be seen from theseresults that thermal resistance characteristics are maintained ataforesaid values While the creep and tensile ductilities become muchhigher, especially the creep ductility value A is increased from lessthan 1% to about 15%.

In the case of 7% Al-Al 0 the creep tests were carried out at 450 C. toyield the following average values:

Creep test at 1000 h.

Rupture stress a 6.2 kg.lmm.a

Total elongation percent (4 diameters) A6 z 4.5%

It can be seen from these results that thermal resistancecharacteristics are maintained at the aforesaid values, while the creepductility increases considerably, namely from less than 1% to about4.5%.

Embodiment 3.(7% Al-AI O projected on Al-tube) The transformation of thebasis material into wire, and the operating conditions during metalprojection are the same as described'above for the first and secondembodiment of the invention. But instead of projecting on a massivebillet core (a bar rotating at 10/ .70 rev/min.) projection was carriedout on a rotating Al-tube (10/ .70 rev./min.) until a billet of about 70mm. outer diameter was obtained. This billet was turned then on a latheto provide a 68.4 mm. outer diameter by a 25.75 mm. inner diameter.Further, this billet was degassed in a vacuum furnace (10* mm. Hg) at atemperature of 600 C. during 20 hours.

The degassed billet tube was then extruded through a die at 575 C. todeliver a helical finned tube.

The extrusion data were:

Container diameter: 70 mm. Container temperature: 550 C. Dietemperature: 540 C. Extrusion ratio: 25

Extrusion speed: 25 m./min.

The mechanical tests were carried out at 450 C. to yield the followingaverage values:

Tensile test (fast traction) Ultimate tensile strength: R=9 kg./mm.

Total elongation percent (5 diameters): A =4% Rapid (fast) burst test at450 C.: Bursting stress o'=8 kg./mm.

Embodiment 4.(7% Al'Algoa projected in parallel to the billets axis)Also in this case, the wire-extrusion and the operating conditionsduring projecting correspond to the above quoted data. But whereas inthe case of the first three embodiments of the invention, projection wascarried out perpendicularly to the billets axis, this time, projectionwas carried out more or less in parallel to said axis onto a discrotating at 30 rev./min. In that way, a massive billet was prepared of70 mm. diameter and 120 mm. of length. The billet was turned down on alathe to 68.4 mm. diameter and mm. of length. Then the billet Wasdegassed in the same way as described for the other cases.

Likewise, the transformation of the billet into a bar of 20 mm. diameterwas carried out according to the data listed above for the embodiments 1and 2.

Creep tests were carried out then at 450 C., which yielded the followingaverage values:

Creep test (at 300 h.)

Rupture stress =53 lrgJmm.

Total elongation percent diameters) A :4%

The elongation before rupture was about 2.5%.

It can be seen from these results, that also in the case of the thirdand fourth embodiments of the invention, the thermal resistancecharacteristics of the material are preserved, while the creep ductilitybecomes much higher.

What we claim is:

1. A method for producing dispersed phase alloys of improved ductilitycomposed of a metal and an oxide of that metal, said process comprisingpulverizing the metal, partially oxidizing the resultant powder,metal-spraying the partially oxidized product on a basis body, saidspraying being carried out at a distance varying from 50 mm. to 250 mm.from the basis body at a temperature of at least 800 C. with time offlight periods of not more than a few seconds thereby providing abillet, removing said billet from the body, and then submitting saidbillet to mechanical working in order to obtain the final mechanicalproperties of the semi-finished or finished product.

2. The method of claim 1, wherein the basis body is rotated during themetal projection operation and the projection direction is perpendicularor oblique to the rotating surface of the body.

3. The method of claim 2, wherein the billet is submitted to thermaldegassing and oxide stabilization in a vacuum furnace.

4. The method of claim 3, Wherein degassing and oxide stabilization iseffected between 550 and 625 C. at a pressure between and 10- mm. Hg forperiods of 10-30 hours.

5. A method for producing dispersed phase alloys of improved ductilityand composed of a metal and oxide of that metal comprising pulverizingthe metal, partially oxidizing the resultant powder, cold pressing theoxidized powder, subjecting the compressed powder to a sintering and avacuum heat treatment, hot pressing the material to form a billet,reducing said billet to wire by wire-extrusion and a wire-drawing,metal-spraying said wires on a basis body, said spraying being carriedout at a distance varying from 50 mm. to 250 mm. from the basis body ata temperature of at least 800 C. with time of flight periods of not morethan a few seconds thereby providing a billet, removing said billet fromthe body, and then submitting said billet to mechanical working in orderto obtain the final mechanical properties of the semi-finished orfinished product.

6. The method of claim 5, wherein the basis body is rotated during themetal projection operation and the projection direction is perpendicularor oblique to the rotating surface of the body.

7. The method of claim 5, wherein the billet is submitted to thermaldegassing and oxide stabilization in a vacuum furnace.

8. The method of claim 7, wherein degassing and oxide stabilization isefiected between 550 and 6-25 C. at a pressure between 10* and 10* mm.Hg for periods of 10'.30 hours.

9. A process for producing dispersed phase alloys of improved-ductilitywhich comprises mixing A1 powder and A1 0 powder, metal spraying theAl-Al O mixture upon a basis body, said spraying being carried out at adistance of from 50 mm. to 250 mm. from the basis body, at a temperatureof a least 800 C., with time of flight periods of not more than a fewseconds, thereby producing an alloy billet, stripping said billet fromsaid body, heating said billet to a temperature of 550 C. to 625 C. at apressure between 10'- and 10- mm. Hg for from 10 to 30 hours todegassify and stabilize the alloy thereof, and then mechanically workingsaid billet to develop the mechanical properties of a semi-finished orfinished product.

10. A method according to claim 9, wherein the metal oxide content ofthe mixture is from 2 to 20% by weight.

11. A method according to claim 1, wherein the alloy is Al-Al O and theA1 0 content is from 2 to 20% by weight.

12. A method according to claim 5, wherein the alloy is Al-Al O and theA1 0 content is from 2 to 20% by weight.

References Cited UNITED STATES PATENTS 3/1961 White et al. 117105.26/1961 Kubera et al. 29528 US. Cl. X.R.

